As is well known in the art, an in-line fuel injection pump for use in a diesel engine has a structure for feeding fuel under pressure. The fuel feeding structure is described below.
The in-line fuel injection pump has a cylinder as a pump element, and the cylinder includes a plunger barrel having a spill port. A plunger is slidable in the plunger barrel and has an inclined plunger reed formed thereon. Fuel is fed under pressure during a period of time until the spill port faces the plunger reed.
Fuel that is metered by the fuel injection pump is injected by an injection nozzle. In the case where the fuel injection pump is connected to the injection nozzle by an injection pipe, the ignition of fuel may be delayed by a time lag that is caused by the flow of fuel in the injection pipe.
As the rotational speed of the engine is increased, the crankshaft angle by which the crankshaft rotates prior to the fuel ignition becomes larger, and the period of time by which the fuel ignition is delayed is so large that the fuel ignition fails to meet the best fuel combustion timing.
To prevent such a phenomenon from occurring, it has been customary to equip the camshaft of the injection pump with an injection advancing mechanism which employs a timer that operates based on centrifugal forces produced by the rotation of the engine.
The injection advancing mechanism is interposed between the crankshaft of the engine and the camshaft of the injection pump. Under centrifugal forces produced when the crankshaft rotates at high speed, a timer weight of the injection advancing mechanism is displaced radially outwardly to advance the phase of the camshaft from an initial position.
In recent years, it has been considered effective to increase the combustion efficiency of a diesel engine for the purpose of reducing the generation of harmful components in exhaust gases.
In view of such a consideration, it has been proposed to increase the pressure under which fuel is injected.
According to the above proposal, fuel is atomized into fine particles when injected under high pressure, and an increased amount of air is introduced into the mist of fine fuel particles to increase the average excess air factor of the fuel mist for thereby forming a good air-fuel mixture.
However, the proposal has suffered the problems, described below, that the present invention is to solve.
In a fuel injection system including the above injection pump, since the plunger of the injection pump is actuated by a cam, the torque required to drive the cam has to be increased for feeding the fuel under higher pressure, and the injection advancing mechanism has to be increased in size because the cam is required to be large in size.
In addition to the increased size of the injection advancing mechanism, the high-pressure feeding of the fuel also poses a problem in that the pressure under which the fuel is injected is not constant because the rotational speed of the engine varies.
Specifically, the fuel injection pressure goes higher when the rotational speed of the engine is higher, and goes lower when the rotational speed of the engine is lower.
The above phenomenon affects the atomization of the fuel. The high-pressure fuel injection is effective to generate a good air-fuel mixture for the reasons described above insofar as the engine rotates at higher speed. On the other hand, no good air-fuel mixture can be formed when the engine rotates at lower speed because the fuel injection pressure is lower.
For increasing the fuel injection ratio of the injection pump when the engine rotates at lower speed, an attempt would be made to increase the fuel injection pressure in the injection pump to achieve the fuel injection ratio in the lower engine speed range. Such an attempt would result in an excessive fuel injection pressure in the injection pipe in the higher engine speed range, and hence would require the injection pipe to be structurally rigid enough to withstand the excessive fuel injection pressure. This would incur an increase in the production cost. Accordingly, following such an effort would not be a real solution to the problems.
Diesel engines with the above fuel injection system emit harmful components that vary in proportions depending on the vehicle speed and the engine load.
More specifically, harmful components in exhaust gases include hydrocarbon (HC), nitrogen oxides (NOx), and substances, known as particulates, composed of hydrocarbon in unburned gases which is attached around soot particles.
The hydrocarbon (hereinafter also referred to as "HC") is generated in a higher proportion in a relatively low speed range or load range. The nitrogen oxides (hereinafter also referred to as "NOx") are generated in a higher proportion in a high speed or load range where the combustion temperature is relatively high. The particulates do not remain when the temperature in the combustion chamber is high, but remain in a relatively high proportion in a low load or speed range because the HC also remains in a large quantity due to a high temperature in the combustion chamber.
The distributor fuel injection pump includes a single plunger that is reciprocally movable to pressurize fuel and also rotatable to distribute fuel to a plurality of engine cylinders.
The number of parts that the distributor fuel injection pump is made up of is relatively small, and the distributor fuel injection pump can be made smaller in size, as compared with the in-line fuel injection pump.
One distributor fuel injection pump is shown by way of example in FIG. 44 of the accompanying drawings. The distributor fuel injection pump has a pump sleeve 01 in which a plunger 02 is slidably and rotatably disposed. When rotative power is transmitted from an engine to the plunger 02, a roller 04 held in rolling contact with a face cam 03 integral with the plunger 02 causes the plunger 02 to slide for pumping the fuel. The roller 04 is supported by a support 05 that is adjusted in a direction R by a hydraulic pressure timer for adjusting fuel injection timing. A spill ring 06 is fitted over the plunger 02. The rate of fuel to be fed by the fuel injection pump can be adjusted depending on the position in which a spill port 07 is opened by the spill ring 06. However, the conventional fuel injection pump structure has suffered the following disadvantages that the present invention is to eliminate:
The distributor fuel injection pump used in the conventional fuel injection system requires various components including a hydraulic pressure timer, a spill ring, and a governor, for adjusting the rate and injection timing of the fuel, and cannot be sufficiently reduced in size.
The conventional hydraulic pressure timer, spill ring, and governor have a relatively narrow control range, and their control characteristics are limited by the rotational speed range of the engine.
In view of the problems that arise when the injection timing and the injection rate are to be established depending on the rotational speed of the engine, it is a first object of the present invention to provide a fuel injection system having an injection pump and an injection nozzle that are connected by an injection pipe, the fuel injection system being relatively simple in structure and capable of reducing harmful components in exhaust gases even when the rotational speed of the engine and the load on the engine vary.
A second object of the present invention is to provide a fuel injection system having an injection pump and an injection nozzle that are connected by an injection pipe, the injection pipe including a branched portion coupled to a solenoid-operated valve for establishing a fuel feed pressure, the fuel injection system being capable of independently controlling the injection timing and the injection rate depending on the rotational speed of the engine, for thereby reducing combustion noise and harmful components in exhaust gases and effecting fuel injection under optimum conditions for better fuel economy.
A third object of the present invention is to provide a fuel injection system having an injection pump and an injection nozzle that are connected by an injection pipe, the fuel injection system being relatively small in size and having a simple structure for metering fuel and establishing a pressurized fuel feed period in a diesel engine having a plurality of cylinders, and also being capable of suppressing the generation of harmful components in exhaust gases and combustion noise.
A fourth object of the present invention is to provide a fuel injection system having a distributor fuel injection pump which is effective to reduce noise and increase responses and controlling capability.
A fifth object of the present invention is to provide a fuel injection system having a modified cam profile for uniformizing the ratio of pilot fuel injection irrespective of its injection timing for stable fuel combustion, the fuel injection system being also capable of optimizing an interval between pilot fuel injection and main fuel injection.